In recent years, there has been a tendency for automotive vehicles to become lighter and smaller and, as a result, to incorporate smaller engines than heretofore. With a small engine operating at low speeds, particularly when idling, pulsating firing impulses produce alternating angular accelerations and decelerations at the input of an assoicated transmission. This induces objectionable gear rattle, which is particularly objectionable in the small manual transmissions incorporated in modern vehicles.
U.S. application Ser. No. 643,731 discloses an anti-rattle device which is self-actuating to become operable when the variations in angular velocity are most objectionable; that is, when the engine is idling, the transmission is in neutral, and the clutch is engaged. That device is similar to a limited capacity spring clutch, but differs therefrom in that it is attached to the first ratio output gear and wrapped around the mainshaft. The spring thus rotates with the first ratio output gear. Relative rotation between the first ratio output gear and the mainshaft is such that there is a tendency for the spring to unwrap when the transmission is engaged in any forward ratio other than first. When the transmission is in first, the first ratio output gear is locked to the mainshaft. There is no relative rotation therebetween, and no tendency for the spring either to wrap or unwrap. When the transmission is in neutral with the clutch engaged, relative rotation between the first ratio output gear and the mainshaft is such that the spring tends to wrap tighter around the mainshaft. The resulting increased friction develops a drag that tends to reduce gear rattle which otherwise would be objectionable in the neutral idle condition. The increased friction also is developed when in reverse, but the resulting inefficiency is tolerable because of the relatively short periods of time when a transmission is engaged in reverse.
It is apparent now that the device may cause a binding condition during engagement of the first ratio output gear. To engage, a synchronizing clutch sleeve is moved, and it applies a load to a blocker ring, which load is transferred to the gear. When the clutch sleeve and the gear are turning at the same angular velocity, the clutch sleeve passes through the blocker ring plane and into engagement with the gear clutching teeth.
Due to random chance, the blocker ring and gear clutching teeth may be in alignment, in which case the clutch sleeve passes through the plane of the gear clutching teeth without contact. However, they may be out of alignment slightly, in which case the clutch sleeve contacts one side or the other of the gear clutching teeth as it passes through. Such contact could cause the gear overrun the mainshaft momentarily. This would activate the anti-rattle device and cause an undesirable binding condition.